1. Field of the Invention
The present invention relates in general to an imaging apparatus, and in particular to an imaging apparatus provided with an OCT function for scanning an examination area of a subject tissue with a signal light, which is a low coherence light, and obtaining an optical tomographic image thereof.
2. Description of the Related Art
There are in use in a variety of medical fields imaging apparatuses that image for observation tissue surfaces of living subjects. If an image obtained by an imaging apparatus is displayed on a monitor or the like, a plurality of people may observe the examination area image. Also, by recording an examination area image, progressive observation and the like will become possible. As these imaging apparatuses, those which utilize electron endoscopes are in wide use. Apparatuses that utilize a pen-form surface examination probe are also known. A conventional electron endoscope is equipped with an imaging element at the distal end of an insertion portion thereof, to be inserted within a body cavity of a patient. It is also often the case that, in a surface examination probe, an imaging element is provided at a distal end of a pen-form probe.
On the other hand, in conventional OCT (Optical Coherence Tomography) apparatuses, in which a low-coherence light is utilized, particularly, OCT apparatuses that obtain an optical tomographic image by measuring the intensity of the interference-light caused by the low-coherence light by heterodyne wave detection are being utilized for obtaining optical tomographic images of the microscopic structure under the fundus of the retina. A detailed description of the aforementioned heterodyne detection OCT apparatus can be found in an article in “O Plus E” Vol. 21, No. 7, pp. 802-804, by Masamitsu Haruna.
According to the aforementioned OCT apparatus: the low-coherence light emitted from a light source formed of an SLD (Super Luminescent Diode) or the like, is separated into a signal-light and a reference-light; the frequency of the signal-light or the reference-light is slightly shifted by use of a Piezo element or the like; the target subject tissue is irradiated with the signal-light and interference is caused between the reflected-light reflected from said target subject tissue at a predetermined depth and the reference-light; the signal strength of the interference signal produced due to said interference is measured by a heterodyne wave detection; and the tomographic data is obtained; wherein, by very slightly moving a movable mirror, etc. disposed above the optical path of the reference-light, causing the length of the optical path of the reference-light to change slightly, the data for a depth of the target subject tissue at which the length of the optical path of the reference-light and the length of the optical path of the signal-light are made to be equal can be obtained.
By utilizing such OCT apparatuses, because the early diagnosis of the depth of penetration of cancer and the like also becomes possible, there is a large demand to obtain an optical tomographic image along with a standard examination area image.
However, in order to employ an imaging apparatus equipped with a surface examination probe and an OCT apparatus, it is necessary to place both said surface examination probe and an OCT detection element in the vicinity of an examination area, thereby requiring a large amount of space in the vicinity of said examination area.
Further, methods of obtaining an optical tomographic image of the interior of a body cavity by utilizing an OCT detection element insertable into the forceps port of an electron endoscope and guiding the signal light as well as the reflected light of the signal light in order employ an imaging apparatus equipped with an endoscope and an OCT apparatus are currently being developed. However, in order to obtain an optical tomographic image by utilizing an OCT detection element inserted into the forceps port of an endoscope, a forceps port must be provided on the endoscope. A problem arises that the insertion portion of an endoscope cannot be made thin. In addition, if implements for performing biopsies or other procedures are to be utilized simultaneously with an OCT detection element, two forceps ports must be provided, further increasing the difficulty in making the insertion portion thin.